Driving Me Crazy (MYQL Help Please)

[noonespecial]

I have a table (links_favorites) with two columns (linkid and userid).

I want to write something that counts the number of matches (in linkid) between two different userids.

So it something that grabs all the linkids from userid A - and then all the linkids from userid B - and then counts all the places where this intersects.

However, I simply can't figure out the best/easiest way to do this.

Could someone help please?

[nighthalk]

I don't have your database to test this. So here you can test it.


<?php
$sql="SELECT linkid, userid, FROM links_favorites WHERE MATCH (linkid,userid)";
$result = mysql_query($sql);
$resultsnumber = mysql_numrows($result);

echo "$resultsnumber";
?>


Let me know if this works.

[noonespecial]

Problem with this is that I need to be able to specify the userids ...

IE: there are 4 matches in LINKID between userid-A and userid-B

Where would I specify those in this example?

--------------- Added 1208335849 at 1208335849 ---------------

$sql="SELECT linkid, userid FROM links_favorites WHERE userid=1083";
$result = mysql_query($sql);
$number1 = mysql_fetch_array($result);

$sql2="SELECT linkid, userid FROM links_favorites WHERE userid=1";
$result2 = mysql_query($sql2);
$number2 = mysql_fetch_array($result2);

$result3 = array_intersect($number1, $number2);

$joined = count($result3);

echo $joined;

Also doesn't work. :(

--------------- Added 1208335899 at 1208335899 ---------------

$sql="SELECT linkid FROM links_favorites WHERE userid=1083";
$result = mysql_query($sql);
$number1 = mysql_fetch_array($result);

$myids=implode(",", $number1);

$sql2="SELECT COUNT(linkid) as count FROM links_favorites WHERE userid=1 AND linkid IN (".$myids.")";
$result2 = mysql_query($sql2);
$number2 = mysql_fetch_array($result2);



Also doesn't work. :(

--------------- Added 1208337252 at 1208337252 ---------------

$fandom = $vbulletin->db->query_read("SELECT *
FROM links_favorites AS links_favorites
LEFT JOIN links_favorites AS favs2 ON (links_favorites.linkid=favs2.linkid)
WHERE links_favorites.userid=".$vbulletin->userinfo['userid']."
AND favs2.userid=".$friend[userid]."
");

$joined= $db->num_rows($fandom);

I think this works ..... ugly.

[MoT3rror]

$linkcount = $db->query_first("
SELECT COUNT(linkid) AS linkcount
FROM links_favorites
WHERE userid IN (1, 2)
");

[Farcaster]

If I am understanding your question correctly and you want to know how many links User 1 and User 2 share, then you could use this query:

SELECT
COUNT(DISTINCT t1.linkid) AS shared_links
FROM
link_favorites t1
INNER JOIN link_favorites t2 ON
t1.linkid = t2.linkid
WHERE
t1.userid = 1
AND t2.userid = 2

Your inclination to use a self-join in your example is pretty close to the mark, except that you could get duplicates and you might as well let MySQL handle the counting. Also, a left join would return all of user 1's links, whether they matched or not.

[Eikinskjaldi]

or you could use a nested query:


select count(distinct linkid) from link_favourites
where userid=1
and linkid in
(select distinct linkid from link_favourites where userid=2)

[noonespecial]

Thank you.